EPS 102 lecture 17

EPS 102 lecture 17 - EPS 102 lecture 17 Thursday March 19th...

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EPS 102 lecture 17 Thursday March 19 th , 2009 Thermohaline Circulation is quite slow. How would density distribution drive flow? There are 2 important factors: temperature, cold things are more dense and tend to sink. Warm things are less dense and rise. Also salinity. We need both of these sources of buoyancy in mind. Heat and salt both drive flow. Chaos: systems may arise in several states and hop from one to the other. Pure water: most normal materials when cooled down get denser. Water is densest at 4 degrees Celsius. This is why ice floats on the surface. Salinity: related to the conductivity of the fluid. Dissolving salt in water= more electrical conductivity. We can measure the conductivity; increasing any of them increases the density (increasing the salinity or conductivity, that is). As you make things colder, you can increase the density and the same is when you increase the Conductivity Temperature Depth. It can measure conductivity, and concentrations of isotopes, etc… Salinity is measured in parts per thousand. Salinity in parts per thousand would be okay if we only took into consideration NaCl, but seawater has more things like Mg, S, K, Ca. If you want to characterize seawater, you have to specify the concentrations of all of these. But we use electroconductivity to get their concentrations. With salt, you have a certain amount of salinity in the surface waters which is the difference between evaporation and rainfall. We see different salinities that tell us where the water came from: the water came from certain levels and salinity can help us infer different water masses. If we know what the temperature and salinity is, we get a density profile (pycnocline) going from surface values to deep values which are highest. Light stuff is on top and heavy stuff is on bottom. If you look at the sound speed, it involves temperature, pressure, etc. . and the sound speed increases in the shallow parts of the ocean as an effect of temperature BUT it also increases as we go down due to increase in pressure. We have a minimum point. Seismic waves that go down into the Earth from the surface, as it goes through faster material it changes direction. The analogy is a band walking along a road and one part of the marching band goes into sand and the wave slows down. The waves tend to turn and come back up so if velocities are going faster as you go down, it turns and comes back up. If the velocity decreases, the wave turns. In the sound wave, a whale calls out to its friend and the wave turns and curves back up due to refraction. Further away from the earthquake you are, the deeper you are sampling. In the ocean, sound goes down and it comes back up to refract. But whale’s sound up to the surface also increases and turns. You get a sofar channel in which sound gets carried. Whales go down to that depth and
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EPS 102 lecture 17 - EPS 102 lecture 17 Thursday March 19th...

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